1. Field of the Invention
The invention relates to a process and apparatus for the separation and treatment of infectious waste in a rapid, cost efficient manner, with materially less environmental impact than the historically practiced art. More particularly, the invention relates to an apparatus and method for the continuous treatment of biologically contaminated medical waste, such as syringes, gowns, bedding, containers, bandages and other liquid or solid materials which may be contaminated with infectious bacterial and viral agents, or with organic contaminants such as chemopharmaceuticals, oxidizable solvents, and the like, in a reactor utilizing gas oxidation. The process and apparatus can simultaneously be used to recover recyclable materials obtained from the incoming waste stream.
2. Description of the Prior Art
The disposition of infectious waste is an issue which has received considerable attention among governmental environmental agencies and the public and within the waste disposal industry. Inappropriate disposal practices, as evidenced by infectious medical waste washing up on the beaches of oceans and lakes, as well as being found in ordinary trash containers in public areas, supports the concern that currently practiced treatment and disposal methods are inadequate to handle, in a safe, cost effective manner, the volume of infectious waste being generated today. A process to treat economically large volumes of infectious medical waste in an environmentally acceptable fashion not heretofore used to treat such waste, is therefore needed.
Historically, most infectious waste has been treated by incineration, with the incineration residue thereafter being landfilled or dumped in the oceans. However, recent studies performed on emissions generated from the combustion of medical waste, even from facilities equipped with advanced air pollution control equipment, have demonstrated consistent emission of priority metals, acid gases, and carcinogenic organics such as 2, 3, 7, 8 furans and dioxin. (United States Environmental Protection Agency, Hospital Waste Combustion Study, December, 1988). It is the potential toxicity of emissions from medical waste incineration which has driven the capital and operating cost of incineration and pollution control equipment beyond the reach of most hospitals needing to replace old, inefficient, uncontrolled units. Controversy relating to incinerator emissions has also resulted in substantial public opposition to the construction of private or commercial incineration facilities. The consequence has been that demand for the treatment of medical waste has exceeded available supply, and commercial incinerators have, in instances, overcharged the generators of medical waste. This creates an even greater potential for illicit disposal.
Another method traditionally used for decontamination involves steam sterilization in autoclaves. However, autoclaves are less appropriate for economically treating large volumes of infectious waste, and their consistent effectiveness on certain microorganisms, given the unpredictable composition and density of medical waste, has not been fully established. Further, autoclaves do not by themselves change the inherent visual appearance of waste, resulting in uncertainty and fear among those persons responsible for its subsequent handling. Many cases have been reported of autoclaved waste being rejected at landfills.
Others have attempted liquid chemical disinfection of medical waste simultaneously with comminution in high speed hammermills. For instance, U.S. Pat. No. 3,926,379 teaches a continuous process for the decontamination of solid items of comparatively small size, such as hypodermic syringes. This material is introduced through a feed tube to a hammermill, along with a disinfectant liquid delivered by pump. Pulverized solid waste then drops to a bag or drawer. Disinfectant drains from the bag and is reused. However, with this device the potential for microbial aerosols exists, as well as the inability to assure that the disinfectant solution has not become neutralized and therefore inactive. Finally, the device is limited to solid, friable objects of small size; it is not suitable for bulk, loose wastes as received from hospitals.
U.S. Pat. No. 4,618,103 discloses a continuous process wherein solid medical waste is treated with disinfectant liquid during comminution in a high speed hammermill. Waste is manually introduced through a rotatable door along with disinfectant solution. After passing through the hammermill, waste drops to a settling/separation tank, from which disinfectant solution is discharged continuously to a sewer, and solid residue is removed manually. As in U.S. Pat. No. 3,926,379, this method appears intended for small, solid objects in limited quantity; it is therefore not suitable for large volumes of medical waste.
U.S. Pat. No. 4,619,409 teaches a continuous process wherein solid medical waste is treated with disinfectant liquid during comminution in a high speed hammermill. Waste material is continuously conveyed to a second conveyor which operates an automatic door ahead of the hammermill. Milled waste drops to a settling/separation tank, from which disinfectant solution is discharged continuously to a sewer, and solid residue is removed manually. The method disclosed by this patent is not readily suitable for tonnage quantities of medical waste, owing to the need for manual removal of milled waste from the settling tank, thereby placing humans in contact with the material.
U.S. Pat. No. 4,578,185 teaches another continuous process wherein solid medical waste is treated with disinfectant liquid simultaneously with comminution in a high speed hammermill.
This system is designed for greater volumes of waste than the previous patents cited which utilize a high speed hammermill. However, as in the previous patents cited above, hammermills are most suitable when applied to friable (breakable) materials, but in practice have not proven efficient or effective in achieving particle size reduction with non-friable materials, such as sheet plastic or woven synthetics, neither of which can easily be fractured at standard conditions. Sheet plastics and woven materials comprise a substantial percentage of contaminated medical waste.
Also, as in the previous patent cited above, there is no ability to assure the effectiveness of decontamination on a continuous basis, and none of these patents provide, by themselves, an efficient method of generating treated, recyclable by-products. Further, as in the other patents cited above utilizing high speed hammermills, treatment and comminution occur simultaneously; no means for controlled contacting with disinfectant over a defined retention period is provided. Finally, as in the previous patents cited, there does not exist the ability to treat other liquid organic wastes typically found among medical waste, for instance chemopharmaceutical materials or solvents, prior to discharge to a municipal sewer.
Applicant's prior U.S. Pat. No. 4,884,756 discloses an apparatus for the treatment of medical waste on a continuous process basis. However, applicant's prior apparatus is not suitable for gas oxidation using a reactor vessel series for the disinfecting of medical wastes, nor is there the ability for improved quality control of the treatment process with applicant's prior apparatus as there is with the continuous treatment process of the instant invention. Finally, the technology disclosed by this prior patent cannot separate the waste stream by component to produce suitably recyclable materials.
Applicant has overcome the above-discussed shortcomings of the prior art by providing a continuous process for separating and disinfecting infectious waste, such as infectious medical waste. The process generally comprises:
(a) introducing bulk unseparated infectious waste material into a receiving container means, said receiving container means adapted for receiving a flow of disinfectant such that said receiving container means remains substantially free of infectious contaminants;
(b) shredding the waste material by a primary shredding means;
(c) separating components of the shredded waste material in a separation tank means having a predetermined fluid level thereby producing at least one waste slurry stream;
(d) transferring the waste slurry stream into a reactor vessel series means;
(e) contacting the waste slurry stream with a disinfecting fluid in the reactor vessel series means for a sufficient amount of time to disinfect the waste slurry stream; and
(f) dewatering the disinfected waste slurry stream to recover solid disinfected waste material for recycling.
In addition, the process of the present invention optionally provides additional shredding means located downstream from the separation tank means for further shredding the waste materials in the waste slurry stream, when and if necessary. The disinfectant preferably comprises ozone in gas phase and/or in aqueous solution.
As noted, other shredding means, such as for example secondary and tertiary shredding means, may be employed if necessary to further reduce the size of particles in the waste slurry stream prior to pumping the same into the reactor vessel means. All of the shredder means utilized in the process of the invention are preferably commercially available low speed, high torque rotary shear shredders. The secondary and tertiary shredders, if employed, are preferably adapted for in-line submerged applications, because these shredders are disposed below the fluid level of the separation tank means.
The waste slurry stream (which may comprise from about 1% to about 10% by weight shredded solids) is pumped for a sufficient amount of time to allow the waste slurry stream to fill the reactor vessel means to a predetermined level.
Ozone gas, in a concentration of from about 0.5% to about 10% by weight, is preferably employed as the disinfecting fluid in the reactor vessel means. In order to maximize contact with the ozone gas, the waste slurry stream may be flowed through a gas contactor, associated with the reactor vessel, in a direction opposite to the buoyancy of ozone gas bubbles in the contactors, although co-current or cross-current flows are equally useful if the residence time and turbulence of the waste slurry in the contactor means is adjusted accordingly. For example, when using counter-current flow, the waste slurry is flowed through the contactor at a rate which preferably exceeds the terminal velocity of the ozone gas bubbles. Ozone gas bubbles having an average diameter of about 1 millimeter or less are preferably utilized.
The disinfection process is preferably monitored continuously by an offgas analyzing means associated with the reactor vessel means, to assure that sufficient disinfecting fluid is introduced into and maintained in the reactor vessel means. Contacting times from about 5 to about 45 minutes have been found to be sufficient to effectively disinfect typical infectious waste materials.
The present invention also contemplates an apparatus for the treatment of infectious waste. The apparatus comprises:
(a) a receiving container means for receiving bulk infectious waste material, said receiving container means being adapted to receive a flow of disinfectant from a disinfectant means for disinfecting the surfaces of said receiving container means;
(b) a primary shredding means in association with the receiving container means, for reducing the particle size of the infectious waste material;
(c) a separation tank means connected to the primary shredding means, for separating components of the shredded waste material and forming a waste slurry stream, the separation tank means having a fluid filling means for filling the tank means to a predetermined level;
(d) a reactor vessel means for disinfecting the waste slurry stream, the reactor vessel means preferably comprising:
(i) at least two reactor vessels, the first of which is disposed in a position to receive the waste slurry stream from the separation tank means and the remainder of which is disposed to communicate in series relationship, with such series commencing with the first reactor vessel, each such reactor vessel having associated therewith a gas contactor; PA0 (ii) a disinfecting fluid generating means connected with each of the contactors, for continuously introducing a disinfecting fluid into the contactor and the reactor vessel means; PA0 (iii) a recirculation port means associated with at least two reactor vessels, for allowing the waste slurry stream to flow through each of the at least two reactor vessels at a rate greater than the slurry generation rate; and PA0 (iv) an analyzing means associated with the reactor vessel means, for continuously monitoring the amount of disinfecting fluid introduced by the disinfecting fluid generating means and the amount of disinfecting fluid utilized in the reactor vessel means; and
(e) dewatering means associated with the reactor vessel means, for recovering solid, disinfected waste material from the disinfected waste slurry.
The apparatus may include secondary and tertiary shredding means, as described above, if needed to provide a waste slurry stream having a further reduced particle size.
The reactor vessel means which forms an essential part of the subject apparatus generally comprises from about 1 to about 10 reactor vessel units connected in series. The number of vessels employed will depend on a number of factors described in detail below. Each reactor vessel includes a gas contactor, which may extend longitudinally from the top of the reactor vessel toward the bottom thereof, where the contactor is in connecting relation with the transfer pump means.
The disinfecting fluid generating means used to disinfect infectious waste according to the present invention preferably comprises an ozone generator. The ozone gas disinfecting fluid may be generated from either compressed air or high purity oxygen.